1. Field of the Invention
The present invention relates to a closure structure with a plug, in which an opening hole of an object to be closed is closed by means of a plug, and especially to such a closure structure, which has a simple structure and ensures a watertight closing condition.
2. Description of the Related Art
With respect to an indicator, which optically detects and indicates specific gravity of electrolyte, which is received in a battery, utilizing relationship between the specific gravity and refractive index of the electrolyte, there has conventionally been known a plug-type indicator, which is to be mounted on an upper lid of the battery. Of the conventional indicators, there has generally been used the indicator in which a ball that floats or sinks in the electrolyte in accordance with variation of specific gravity and an upper level of the electrolyte is disposed in a lower portion of a plug member, which is formed of a transparent material and is immersed into the electrolyte. In such an indicator, light entering from the upper side of the plug member is made reflect perfectly from a predetermined reflecting surface to enter a position in which the ball is disposed, and light, which is reflected from the ball or pass through it, is made again reflect perfectly from the reflecting surface to return the light to the upper side so as to provide images, which are different in color and indicate variation of the specific gravity and the upper level of the electrolyte.
When the plug member is fitted into an opening hole of an object to be closed, for example, such an indicator is mounted on the upper lid of the battery, there may be a gap between the object to be closed and the plug member, leading to leakage of liquid received in the object to be closed. In order to prevent such a problem, there has conventionally been used a closure structure, which permits to seal the gap between the object to be closed and the plug member to provide a watertight closing condition.
An example of such a conventional closure structure is shown in FIG. 7. FIG. 7 is a schematic descriptive view of the conventional closure structure.
The conventional structure as shown in FIG. 7 has a structure in which a plug member 102, which has a plurality of flange portions formed on the outer periphery of the plug member 102 so as to extend outward, is fitted into an opening hole 101 of an upper lid 100 of a battery serving as an object to be closed, thus closing the opening hole 101 by means of the plug member 102. The flange portions 102a of the plug member 102 are formed of the same material as the upper lid 100 and have an outside diameter, which is slightly larger than the diameter of the opening hole 101. Forcedly pressing the plug member 102 into the opening hole 101 causes the flange portions 102a to be urged strongly against the upper lid 100, while being deformed, thus making it possible to secure firmly the plug member 102 to the upper lid 100 and prevent leakage of liquid received in the battery.
In the conventional closure structure having the above-described structure, it is difficult to control uniformly deformation of the flange portions 102a in the opening hole 101. As a result, a part of the outer periphery of the flange portion 102a may not come into contact with the upper lid 100, thus causing a gap. Such a gap makes it impossible to maintain the watertight condition, thus causing leakage of liquid as received and leading to occurrence of serious problems.
Alternatively, there also exists the other conventional closure structure as shown in FIG. 8, in which a plug member 102 on the outer periphery thereof a seal member 103 is mounted, is screwed into an upper lid 100 so as to bring the seal member 103 into contact with the plug member 102 and the upper lid 100, thus closing an opening hole 101.
In this case, the seal member 103 comes surely into contact with the plug member 102 and the upper lid 100, thus providing a sufficient watertight condition. However, formation of screwed portions on the upper lid 100 and the plug member 102 makes the structure complicated. In addition, the screwing operation of the plug member 102 into the upper lid 100 requires much labor in comparison with the case where the plug member 102 is forcedly inserted into the upper lid. Consequently, the cost of the second conventional closure structure is relatively high.
An object of the present invention, which was made to solve the above-mentioned problems, is therefore to provide a closure structure with a plug member, has a simple structure with a seal member, thus providing a reliable watertight condition, and permits an easy and rapid fitting operation of the plug member.
In order to attain the aforementioned object, a closure structure of the present invention comprises:
an object to be closed with a plug member, said object to be closed having an opening hole formed thereon;
a plug member to be inserted into said opening hole; and
a seal member disposed on an outer periphery of said plug member, said seal member being formed of a ring-shaped elastic member, said seal member being to be brought into contact with said object to be closed and said plug member so as to close said object to be closed,
wherein:
at least an insertion portion of said plug member, which is to be inserted into said opening hole, is smaller than said opening hole, said insertion portion being provided at an outer periphery of a predetermined portion thereof with a seal member-receiving groove, which extends continuously in a circumferential direction of said insertion portion and has a predetermined depth, and said seal member-receiving groove being provided at a predetermined portion thereof, which is placed on a rear side relative to an insertion direction of said insertion portion, with a seal member-seating portion, which has an outer surface with a predetermined diameter, which is smaller than that of said opening hole by a predetermined length and larger than that of a bottom of said seal member-receiving groove; and
said seal member has a cross-sectional shape, which can be fitted into said seal member-receiving groove of said plug member, said seal member having an outer diameter, which is larger than a diameter of said opening hole in a mounting state into said seal member-receiving groove, said seal member having an elastic deformability by which said seal member, to which an external force is applied, can be deformed so that a thickness thereof in an axial direction reaches at least said predetermined length, and said seal member having opposite end faces in the axial direction, which serve as contact surfaces coming into contact with said object to be closed with the plug and said seal member-seating portion of said plug member.
According to the features of the first aspect of the present invention, the plug member is provided on its outer periphery with the seal member-receiving grove portion for mounting the seal member and with the seal member-seating portion having the predetermined outside diameter. Inserting the plug member, to the seal member-receiving groove portion of which the seal member is fitted, into the opening hole causes the outer peripheral portion of the seal member to be elastically deformed from the initial position in the seal member-receiving groove portion toward the opposite direction to the insertion direction of the plug member, under reaction force applied from the object to be closed to the outer peripheral edge of the end face of the seal member in the axial direction thereof, due to insertion force applied to the plug member, while keeping the inner peripheral edge of the end face of the seal member in contact with the seal member-receiving groove portion. The opposite end faces of the seal member in the axial direction thereof, which have been kept in a non-deformed state before insertion of the plug member into the opening hole, come into close contact with the object to be closed and the seal member-seating portion, respectively, after insertion of the plug member into it. Accordingly, when the plug member having the seal member the size of which is so large as to provide a sufficient sealing property is inserted into the opening hole, the seal member is elastically deformed so that the outer peripheral portion of the seal member extends from the initial position in the seal member-receiving groove portion toward the seal member-seating portion, thus preventing the seal member from sliding relative to the object to be closed and decreasing frictional resistance during an inserting operation of the plug member. In addition, the opposite end faces of the seal member come into close contact with the object to be closed and the seal member-seating portion, respectively, thus ensuring a sufficiently large contact area to provide a sealing condition. As a result, it is possible to insert easily the plug member into the opening hole as well as provide a reliable watertight condition.
In the second aspect of the present invention, said plug member may be provided on a rear side of said seal member-seating portion relative to the insertion direction of said plug member with a seal member-restricting portion, which has an outside diameter larger than that of said seal member-seating portion.
According to the feature of the second aspect of the present invention, the plug member is provided with the seal member-restricting portion, which has the outside diameter larger than that of the seal member-seating portion, so that the seal member-restricting portion prevents the seal member from moving relative to the plug member in the opposite direction to the insertion direction of the plug member. It is therefore possible to prevent the seal member from moving excessively relative to the plug member in the opposite direction to the insertion direction of the plug member so as to be apart from the seal member-receiving groove portion, thus holding the seal member in the seal member-seating portion in an appropriate manner. Pulling the plug member from the opening hole causes the seal member to move from the seal member-seating portion to the seal member-receiving groove portion, thus decreasing sliding resistance of the seal member relative to the inner surface of the object to be closed and making it possible to carry out easily a removing operation of the plug member.
In the third aspect of the present invention, said plug member may be provided on a front side of said seal member-seating portion relative to the insertion direction of said plug member with a seal member-urging projection having a flange-shape, said seal member-urging projection having a diameter, which is larger than said seal member-seating portion, said diameter of said seal member-urging projection being predetermined so as not to prevent said seal member from moving from said seal member-receiving groove portion to an outer surface of said seal member-seating portion.
According to the feature of the third aspect of the present invention, the plug member is provided with the flange-shaped seal member-urging projection, which has the diameter larger than the seal member-seating portion. The seal member is more strongly pressed between the seal member-urging projection and the object to be closed in comparison with the other portion, to be elastically deformed, so that the seal member strongly comes close contact with the outer peripheral surface of the seal member-urging projection and the object to be closed, under restoring force in accordance with deformation of the seal member. It is therefore possible to enhance the sealing property over the entire circumference of the seal member, while maintaining the compact structure of the sealed portion without substantially increasing the contact area of the seal member with the plug member and the object to be closed. In addition, it is possible to ensure the reliable watertight condition, even when there occurs variations in size of the opening hole of the object to be closed.
In the fourth aspect of the present invention, said seal member, which is kept in a non-fitting state to said plug member, may have a cross-section so that a thickness on an inner peripheral side of said seal member in the axial direction thereof is larger than a thickness on an outer peripheral side thereof.
According to the feature of the fourth aspect of the present invention, there is used the seal member having the cross-section so that the thickness on the inner peripheral side of the seal member in the axial direction thereof is larger than the thickness on the outer peripheral side thereof. The seal member is more strongly pressed at the front side of thereof in the insertion direction of the plug member, in which the above-mentioned inner peripheral side is placed in the closed state, in comparison with the other portion, to be elastically deformed, so that the seal member strongly comes close contact with the outer peripheral surface of the seal member-seating portion and the object to be closed, under restoring force in accordance with deformation of the seal member. It is therefore possible to enhance the sealing property over the entire circumference of the seal member, while maintaining the compact structure of the sealed portion without substantially increasing the contact area of the seal member with the plug member and the object to be closed. In addition, it is possible to ensure the reliable watertight condition, even when there occurs variations in size of the opening hole of the object to be closed.